The invention relates to an improved method of producing binary self condensation products of phenols. It is well-known in the art that substituted phenols can be oxidized to yield self-condensation products, especially diphenoquinones and biphenols. The diphenoquinones are useful antioxidants. Biphenols are useful antioxidants, stabilizers and intermediates for the synthesis of various polymers, especially polyesters.
In U.S. Pat. No. 4,195,189, a one-step process for the oxidative coupling of phenols is described wherein molten phenols are combined with an oxidizing agent which is activated copper oxide. The copper oxide was employed in about equal or greater molar ratio with the phenolic compound. In this process the copper oxide is employed not as a catalyst but as a source of oxygen as no oxygen or oxygen-containing gas is otherwise present during the reaction.
In German Pat. No. 536,277, the oxides of copper, manganese and lead were employed in the oxidative reaction of phenol. The reaction product, however, was most probably a polymeric material as it was described as a light grey amorphous precipitate without a sharp melting point which sintered to a brown mass at 120.degree. C. to 130.degree. C. Diphenoquinone is a highly colored crystalline material which melts at about 165.degree. C.